Abstract:In order to study the difference of drought and flood in the middle and lower reaches of the Yangtze River under different intensities of La Niña events, the research area were divided into four regions(northwest, central, south and east)by using the method of rotating empirical orthogonal function(REOF). Based on multivariate ENSO index(MEI), the La Niñ a events from 1961 to 2014 were extracted, and the standard precipitation evapotranspiration index(SPEI)was used to evaluate the drought and flood grades. The results show that different intensities of La Niña events have different influences on the frequency, intensity and spatial and temporal distribution of drought and flood in different regions. During the duration of strong events, severe drought is prone to occur in northwest region, and severe floods are prone to occur in other regions. After strong events, mild floods may occur in northwest region and moderate or more droughts may occur in other regions. During the duration of moderate events, the frequency and intensity of flood in northwest region are slightly higher than that of drought in other regions. After moderate events, the frequency and intensity of flood in northwest region are very large, and the frequency and intensity of drought in other regions are very large. Weak events have little influence on drought and flood, and have reverse change characteristics in south and north parts, while southern drought and northern flood. The reasons for the difference in frequency, intensity and distribution of drought and flood are related to the intensity of water vapor transport and vertical movement which are affected by different levels of La Niña events.